After a failed pursuit for Aberdeen boss Derek McInnes, Sunderland are still searching for a replacement for David Moyes, who resigned at the end of last season following the club's relegation to the Championship.
However, it has been revealed that they can talk with Grayson after Preston released a statement to confirm Sunderland's approach.
It read: "Preston North End have today been contacted by Sunderland Football Club to ask permission to speak to Simon Grayson in relation to their vacant managerial position.
"Having spoken to Simon, he has asked permission to speak to the Black Cats and therefore the club had no option but to allow these conversations to take place, with a compensation package already guaranteed in his contract.
"Whilst these talks are ongoing, Steve Thompson will be in charge of first team affairs. The club will make no further comment at this stage."
Grayson has been at Deepdale since 2013, and he has established the club at the second tier of English football with successive 11th-place finishes in the Championship.